The Darksteel set is everything you loved about Mirrodin and more: more equipment, more artifacts, more abilities, and even more cards. Darksteel is the first "small" Magic expansion to release with 165 cards. Among them, you'll find artifacts that are indestructible--which means just what it says: destruction effects don't send them to the graveyard. And if its an indestructible creature, damage won't do the job, either.